The technologies relating to nanomaterials are being applied to various industrial fields, and it is known that the application of these technologies to general polymers can improve their physical, chemical, and thermal characteristics.
In particular, it is reported that the nanocomposite material, which is a material reinforced with nano-sized raw materials, has excellent physical properties compared to general composite materials (R. A. Vaia, Polymer Nanocomposites Open a New Dimension for Plastics and Composites, The AMPTIAC Newsletter, 2002, 6, 17-24), and also that the nanocomposite material show an increased elastic modulus as well as increased strength (M. M. O. Seydibeyoglu et al., Composites Science and Technology, 2008, 68, 908-914). It is known that the increase in strength could be attributed to the increase in specific surface area of nanomaterials, and the decrease in the interfacial defects between the nanomaterial and the matrix polymer, compared to the composite material reinforced with micro-sized raw materials (M. Sternitzke et al., Journal of the American Ceramic Society, 1998, 81, 41-48).
Meanwhile, cellulose is the most abundant natural polymer among all organic compounds present in nature. It can be obtained from renewable materials, and has a biodegradable property by which it can be decomposed in soil and returned to nature, unlike the conventionally used petroleum-based polymers. Recently, with a growing demand for the environmentally friendly polymer materials due to serious environmental issues being raised, intensive studies have been performed to develop cellulose raw materials and products thereof to replace petroleum-based functional polymers (G. Siqueira et al., Polymer, 2010, 2, 728-765).
In particular, nanostructured fibrillated cellulose can be used for composite materials as a reinforcing material, because it has high elastic modulus of 150 GPa to 200 GPa and high strength of 5 GPa. The nanostructured fibrillated cellulose has excellent physical properties compared to Kevlar® fibers, a well-known super fiber. Moreover, the nanostructured fibrillated cellulose has a nano-scale diameter, which is smaller than that of the general carbon fibers and glass fibers (diameter of 10 nm to 100 nm). Further, it has a low thermal expansion coefficient (0.1 ppm K−1), is economical, recyclable, lightweight, has low energy consumption, and has excellent processability. Accordingly, there is a high possibility that cellulose nanofiber can replace the glass fiber, which is a core material in the composite material industry, by adjusting its diameter (nano-sized) and aspect ratio (L/D), based on its excellent characteristics such as high crystallinity, tensile strength, and elastic modulus.
The nanomaterial manufactured from 100% cellulose nanofibers having the advantages described above has been reported to have excellent physical properties compared to the ordinary steel or magnesium alloys. However, since the above composite material consists only of 100% cellulose, long-term drying and compression are required due to the process characteristics, and it has been known that the composite material can be manufactured only in the form of a sheet. Additionally, the above composite material has no thermoplasticity, and thus there is a problem in that the material cannot be formed into various shapes (Marielle Henriksson et al., 2008; Istva'n Siro et al., 2010).
However, the thermoplastic and thermosetting composite material reinforced with the cellulose nanofiber has a high potential to be used as an environmentally friendly high-performance new material for next generation, capable of overcoming the limitations of the existing glass fiber-reinforced composite materials. With the development of modern industry, there has been a demand for products with low weight and high strength. Thus the cellulose nanofiber composite material having high performance and high function can expand its applications as a core material to the industrial fields, such as electronics, transporting devices (e.g., automobiles, aircraft, ships, etc.), civil engineering, construction, environment, etc., the defense industry, and prosthetic devices in the medical industry.
Additionally, in the 21st century, much research and developments have continuously focused on a technical field of green nanocomposites, which is a new converging technology of nanotechnology and composite material technology, as a method for resolving environmental, energy, and resource problems. It is highly likely that the cellulose nanofiber composite will have a solid position as a new high-performance composite material surpassing the limitations of existing materials due to its environmental friendliness, cost effectiveness, and sustainability for the next generation. The green composites with such various and excellent physical properties can ultimately provide a base for fundamental technologies to obtain advanced multi-functional materials having mechanical functions of high strength and high elastic modulus, electric and thermal conductivities, low thermal expansion coefficient, etc., which cannot be obtained from the conventional materials.
However, the research and development of thermoplastic composites using the cellulose nanofiber is still in its early stages.
Accordingly, the present inventors have completed the present invention relating to a multi-layered composite material comprising the thermoplastic matrix polymer and the nanofibrillated cellulose having physical properties superior to glass fiber.